1. Field of the Invention
This invention relates to electric heaters used in microsystems, systems, and more particularly to chip-scale heaters used for vapor cell interrogation systems.
2. Description of the Related Art
Advances in microelectromechanical systems (MEMS) have enabled a variety of miniaturized and chip-scale atomic devices used in, for example, gyroscopes, magnetometers and chip-scale atomic clocks (CSAC). With reduced system dimensions come many advantages, including lower operating power and reduced manufacturing cost for the finished device. Of primary importance in many of these MEMS applications, is an atomic vapor cell for use as a frequency-defining element, rather than traditional quartz-crystal resonators, for improved frequency stability.
As is typical for atomic vapor cells during their manufacture, the vapor cell is charged with a sample material that later produces an interrogation gas during heating and subsequent operation. Common sample material examples for atomic vapor cells include rubidium (Rb) and cesium (Cs). The vapor cell is permanently sealed after charging, often using anodic bonding between a silicon substrate containing an interrogation cell enclosing the sample material and a transparent window through which the gas is interrogated after heating. Heaters are typically used to maintain suitable vapor pressure of the sample material in the vapor cell and can be positioned adjacent the gas interrogation cavity of the vapor cell to heat the enclosed sample material. Because the solid form of sample materials such as rubidium and cesium tend to migrate and condense at the coldest portions of the vapor cell, window heaters may be placed directly on the entrance and/or exit windows of the vapor cell to create a suitable thermal profile for reduction of solid sample material buildup over the aperture portion of such windows. Typical window heaters may consist of wire heaters spaced adjacent the aperture portion of the windows or transparent window heaters that may or may not cover the aperture, itself.